1. Field of the Invention
The present invention relates to a carrier and a chemical mechanical polishing (CMP) apparatus for uniformly polishing the surface of a rotating wafer or other workpiece while pressing the workpiece against a polishing pad of a platen.
2. Description of the Related Art
FIG. 15 is a sectional view of a carrier of a general CMP apparatus.
As shown in FIG. 15, a CMP apparatus is provided with a carrier 100 and with a platen 110 to which a polishing pad 111 is attached. By making the carrier 100 and the platen 110 rotate by a rotating mechanism while supplying a polishing solution in a state with the wafer W pressed against the platen 110 side by a carrier base 101 of the carrier 100, the surface of the wafer W is polished by the polishing pad 111.
Further, this CMP apparatus polishes the wafer W by the back side reference polishing system. Thus, a backing pad 102 is attached to the carrier base 101 and the surface of the wafer W is polished with the backing pad 102 in contact with the back surface of the wafer W.
Even if the sectional shapes of the backing pad 102 and the polishing pad 111 are uniform, there is sometimes warping or undulations in the wafer W itself. As opposed to this, the CMP apparatus shown in FIG. 15 is not structured to deal with such warping or undulations in the wafer W, so it is not possible to uniformly press the surface of the wafer W as a whole.
Therefore, the carrier of the CMP apparatus of the air pressurizing system shown in FIG. 16 has been devised.
A carrier 300, as shown in the figure, provides a ring-shaped projecting portion 302 at the outer peripheral portion of the bottom surface of a carrier base 301. By using a double-sided adhesive tape 304 to attach a backing pad 307 to the bottom surface of the projecting portion 302, a pressure chamber 306 is defined.
In this configuration, air arriving through air holes in the carrier base 301 is introduced into the pressure chamber 306 to uniformly press the wafer W through the backing pad 307 by the air pressure in the pressure chamber 306.
The above CMP apparatus of the related art, however, suffered from the following problems.
In the carrier 300 of the CMP apparatus according to the above related art, it is possible to press the entire surface of the wafer W by a uniform air pressure, but there was a large range of over polishing at the outer peripheral portion of the wafer W and the yield was remarkably poor.
FIG. 17 is an enlarged sectional view of the state of over polishing.
As shown in FIG. 17, this carrier 300 is structured with the wafer W covered by the backing pad 307 adhered to the projecting portion 302 of the carrier base 301, so if a downward pressing force is applied to the carrier 300 during the polishing work, the outer peripheral portion of the backing pad 307 will be pulled downward by the projecting portion 302.
Therefore, a tension T occurs at the outer peripheral portion of the backing pad 307 and a pressure of the vertical component T1 of the tension T is applied to the outer peripheral portion of the wafer W in addition to the air pressure P.
As a result, the polishing rate of the outer peripheral portion of the wafer W becomes remarkably larger than the polishing rate of the other portions, the range of over polishing L becomes as larger as 10 mm to 20 mm, and the yield of the wafer W ends up becoming remarkably poor.